PCB Fabrication
Also: bare board fabrication, printed circuit board fabrication, PCB manufacturing, printed wiring board, PWB, bare PCB, multilayer PCB, circuit board fabrication, HDI PCB, flex PCB, rigid-flex PCB, quick-turn PCB
PCB fabrication makes the bare board: copper-clad laminate is imaged, etched, laminated, drilled and plated into single-sided to 30-layer boards, to IPC-6012.
273 shops tagged PCB fabrication among 843 electronics manufacturing companies in the Noramark directory
PCB Fabrication shops by state
A multilayer board starts as thin sheets of copper-clad laminate called cores. Each inner-layer core is coated with photoresist, exposed by laser direct imaging or through a phototool, developed and etched so that only the circuit pattern remains, then checked by automated optical inspection. The cores are stacked with sheets of partly cured glass and resin (prepreg) and outer copper foils, and pressed under heat and vacuum into one panel. Holes are drilled mechanically, or by laser for microvias, and the hole walls are made conductive and electroplated with copper, which connects the layers: the plated through-hole. The outer layers are then imaged, plated and etched, covered with solder mask, given a surface finish on the exposed pads, printed with legend (silkscreen), electrically tested for opens and shorts against the netlist, and routed or scored out of the panel.
Single-sided and double-sided boards skip lamination. High-density interconnect (HDI) boards add laser-drilled microvias, blind and buried vias and repeated lamination cycles to route fine-pitch BGAs. Flexible circuits are built on polyimide film with a coverlay in place of solder mask, and rigid-flex combines rigid and flexible sections in one lamination. Metal-core boards bond a thin dielectric and copper layer to an aluminum plate to pull heat out of LEDs and power devices. Controlled-impedance boards hold trace width, dielectric thickness and copper thickness so that a trace measures, for example, 50 ohms single-ended or 100 ohms differential, usually within ±10%, verified on test coupons.
Bare boards are built and accepted to IPC-6012 for rigid boards and IPC-6013 for flex and rigid-flex, and inspected visually against IPC-A-600. There are three classes. Class 2 is the commercial default. Class 3, for high-reliability products, requires more copper in the plated holes (an average of 25 µm, 0.001", against 20 µm, 0.0008", for Class 2) and does not allow a drilled hole to break out of its pad. Laminates are specified by IPC-4101 slash sheet, or simply as FR-4 with a glass transition temperature (Tg): about 130-140 °C for standard material and 170 °C or higher for high-Tg material, which lead-free assembly and thick multilayers usually need. Boards for UL-listed products need a UL-recognized fabricator and a flammability rating, typically 94V-0.
Fabricators publish their capabilities as a table: minimum trace and space, minimum drill, aspect ratio, layer count, copper weights and finishes. Staying inside the standard column of that table keeps a board cheap and fast. Each step into the advanced column (finer lines, smaller holes, more lamination cycles, special laminates) narrows the number of shops that can build the board and raises its price and lead time.
At a glance
| Typical tolerances | Standard capability at most U.S. fabricators: 0.10-0.125 mm (0.004-0.005") minimum trace and space on 1 oz copper, with 0.075 mm (0.003") as an advanced option; minimum mechanical drill 0.15-0.2 mm (0.006-0.008"); laser microvias about 0.1 mm (0.004"). Finished plated-hole diameter ±0.075 mm (±0.003"); non-plated holes ±0.05 mm (±0.002"). Routed board outline ±0.13 mm (±0.005"), looser on V-scored edges. Overall thickness ±10%. Controlled impedance ±10% standard, ±5% with care. Bow and twist within 0.75% on boards that carry surface-mount parts, per IPC-6012. These figures vary by shop, so check the fabricator's capability table. |
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| Size limits | Boards are built on production panels, commonly 457 x 610 mm (18 x 24") with other sizes in use; the usable area inside the panel border sets the largest single board, roughly 400 x 550 mm (16 x 22") at most shops, and larger backplanes are a specialty. Two to twelve layers are routine everywhere; 20 to 30 layers and above come from shops equipped for high layer counts. Finished thickness runs from about 0.2 mm (0.008") for thin boards and flex to 3.2 mm (0.125") and thicker for backplanes, with 1.6 mm (0.062") standard. A drill aspect ratio (board thickness to drilled hole diameter) of 8:1 to 10:1 is standard, and higher is an advanced capability. Copper weights of 0.5-3 oz are common; heavier copper is available at fewer shops. Much high-volume commodity production is offshore, while U.S. fabricators concentrate on quick-turn, high-mix, defense (ITAR) and advanced-technology boards. |
| Surface finish | The pad finish protects the exposed copper and sets solderability and shelf life. Lead-free HASL is the low-cost default but leaves uneven pads. ENIG gives flat pads for fine-pitch and BGA parts: about 3-6 µm (120-240 µin) of nickel under 0.05-0.1 µm (2-4 µin) of gold. Immersion silver and immersion tin are flat and economical but more sensitive to handling and storage. OSP is the cheapest flat finish and has the shortest shelf life. ENEPIG suits wire bonding, and hard electroplated gold is used on edge fingers and contacts. Solder mask is green by default with other colors available, and legend is printed in white ink by screen or inkjet. |
| Lead time | Quick-turn prototypes of simple 2- to 6-layer boards in 1-5 business days at a premium; standard lead time is about 2-3 weeks for multilayer boards and 3-5 weeks for HDI, rigid-flex, heavy copper or special laminates. Laminate that is not in stock and each extra lamination cycle add time. Offshore production orders add transit time. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
FR-4 glass-epoxy laminate is the default, in standard-Tg (about 130-140 °C) and high-Tg (170 °C and up) grades, with halogen-free versions available. RF and high-speed boards use low-loss laminates such as PTFE-based and hydrocarbon-ceramic materials, often combined with FR-4 in a hybrid stackup. Flexible circuits use polyimide film with rolled-annealed or electrodeposited copper. Metal-core boards use an aluminum base, occasionally copper. Copper foil is specified by weight: 0.5, 1 and 2 oz per square foot are about 17, 35 and 70 µm thick, with heavier copper for power boards. Pad finishes are lead-free HASL, ENIG (electroless nickel with immersion gold), immersion silver, immersion tin, OSP, and hard gold on edge-connector fingers. Solder mask is a liquid photoimageable coating, green by default.
What drives the cost
- Layer count and lamination cycles: each added pair of layers, and each extra lamination for blind or buried vias, adds process steps
- Board area and panel utilization: the price follows how many boards fit on a production panel
- Feature size: trace and space below about 0.1 mm (0.004"), small drills and high aspect ratios lower yield and narrow the choice of shops
- Laminate: high-Tg FR-4 costs a little more; low-loss RF laminates and polyimide flex cost several times more
- Finish and extras: ENIG, hard gold fingers, controlled-impedance testing, via fill, back-drilling, edge plating
- Quantity and lead time: setup and tooling charges dominate small lots, and quick-turn service carries a premium
- Class and documentation: IPC Class 3, microsection reports, first article reports, ITAR handling
When to use it
- Any electronic product that needs a custom circuit board, from prototype to production
- Multilayer, controlled-impedance, HDI, flex and rigid-flex designs
- Quick-turn prototypes that prove a layout before committing to volume
- Boards that must be built in the U.S.: ITAR and defense work, or short supply chains
- Replacing point-to-point wiring with a board to cut assembly labor and wiring errors
When not to
- When you want populated boards from one source: order turnkey from a PCB assembler, which buys the bare boards
- Connections that flex continuously or run between enclosures: a flex circuit, a cable or a wire harness
- Currents beyond what heavy copper carries economically: bus bars or wiring
- Designs outside the fabricator's published capabilities: ask for a manufacturability review before ordering
Design tips
- Design to the fabricator's standard capabilities, not its limits: 0.125-0.15 mm (0.005-0.006") trace and space and 0.25-0.3 mm (0.010-0.012") drills cost less and yield better.
- Send Gerber (RS-274X or X2) or ODB++ data with NC drill files, a fabrication drawing and a stackup; state material, Tg, finished thickness, copper weight per layer, pad finish, solder mask and legend colors, and IPC class.
- Keep the stackup symmetric about its center and balance the copper across layers to limit bow and twist.
- For controlled impedance, give the target, the tolerance and the layers, and let the fabricator adjust trace widths to its own materials.
- Keep annular rings generous: a pad at least 0.25-0.3 mm (0.010-0.012") larger than the finished hole for Class 2, and more for Class 3.
- Specify holes by finished diameter, say whether each is plated, and keep the aspect ratio under about 8:1.
- Keep copper at least 0.25-0.5 mm (0.010-0.020") back from routed edges and farther from V-score lines.
- Ask the assembler how it wants the boards panelized (rails, fiducials, tabs or V-score) before ordering bare boards.
Frequently asked questions
- What is the difference between PCB fabrication and PCB assembly?
- Fabrication makes the bare board: the laminate, copper traces, plated holes, solder mask and legend. Assembly solders the components onto it and tests the result. They are different processes, often at different companies. A turnkey assembler orders the bare boards from a fabricator on your behalf.
- What is IPC-6012?
- The IPC qualification and performance specification for rigid printed boards. It sets requirements for plating thickness, annular ring, conductor width and spacing, dielectric thickness, solder mask and reliability testing in three classes: Class 2 is the commercial default and Class 3 is for high-reliability products. IPC-6013 covers flex and rigid-flex boards, and IPC-A-600 illustrates the visual acceptance criteria.
- What files do I send to a PCB fabricator?
- Gerber files (RS-274X or X2) for every copper, solder mask, paste and legend layer, an NC drill file, the board outline, and a fabrication drawing with the stackup, material, thickness, copper weights, finish, colors, tolerances and IPC class. ODB++ or IPC-2581 packages carry the same data in one file. An IPC-D-356 netlist lets the fabricator check its tooling against your design.
- Which PCB surface finish should I choose?
- ENIG for fine-pitch and BGA parts, flat pads and long shelf life. Lead-free HASL for low-cost boards with larger parts. Immersion silver or OSP for cost-sensitive boards that will be assembled soon after fabrication. Hard gold for edge connectors. Ask the assembler whether it has a preference.
- What is FR-4, and what does Tg mean?
- FR-4 is a flame-retardant laminate of woven glass cloth and epoxy, the base material of most rigid boards. Tg, the glass transition temperature, is where the resin softens and expansion through the thickness rises sharply: about 130-140 °C for standard FR-4 and 170 °C or more for high-Tg grades. Lead-free soldering, thick boards and high layer counts usually call for high-Tg material.
